Foamed polymeric compositions are well known in the art and are being used widely in industry for a variety of purposes.
Although compositions comprising selectively hydrogenated block copolymers of monovinyl aromatic hydrocarbon and conjugated diene have shown interesting properties, it has appeared that the until now available foamed compositions did not meet the present combination of required properties which are necessary for the efficient manufacture of modern foamed articles, e.g. foamed weather seal articles for automotives, ships, aircrafts and the like. The presently required properties include a foam density in the range of from 0.3 to 0.8 103 kg/m3 and preferably from 0.4 to 0.6 103 kg/m3; a reduction of foam density in the range of from 25% to 70%, and preferably in the range of from 33% to 55%; a Shore A hardness <70 and preferably <65, and a compression set at 100° C. of below 70% and preferably below 55%, (measured on a non-foamed injection moulded test plate, 6 mm thickness).
It has been found that relatively high molecular weight, selectively hydrogenated block copolymers of monovinyl aromatic hydrocarbon and conjugated diene, i.e. having a total molecular weight of at least 350,000, were only foamable to acceptable density reductions when combined with an oil and large amounts of a polyolefin, which caused the final articles to show a too high hardness.
On the other hand it has been found that relatively low molecular weight selectively hydrogenated block copolymers of monovinyl aromatic hydrocarbon and conjugated diene, i.e. having a molecular weight of up to 180,000, could be foamed with smaller amounts of or even without polyolefin. However, an important drawback of said foamed compositions was the bad heat resistance.
It was also known from e.g. U.S. Pat. No. 6,221,964 to manufacture foamed compositions, comprising thermoplastic vulcanizates, which had been mechanically foamed with water or other physical blowing agents.
In general, said foamed compositions had been derived from EPDM, polyolefin and more in particular polypropylenes and oil, by mixing in an extruder with a cross linking agent as main component.
A known disadvantage of said foamed compositions derived from thermoplastic vulcanizates was that they were rather hygroscopic and showed an unattractive balance between water absorption and tear resistance. They therefore could not be applied as weather seal articles.
From U.S. Pat. No. 4,764,535 and U.S. Pat. No. 4,677,133 elastomer compositions were known which could be foamed into elastomeric cellular products. The elastomeric compositions comprised a mixture of two thermoplastic rubber compounds, a nucleating agent for enhancing the hydrophilic structure, an unstable detackifying resin and optionally polybutene and/or amorphous polypropylene. However, the final properties of the foamed articles could not meet the present requirements and in particular the heat resistance appeared to be insufficient.
From EP 0875526 A elastic foams were known which were prepared from a reprocessable blend of a thermoplastic vulcanizate and an elastic thermoplastic polymer, comprising either one block copolymer, having 2 or more poly(styrene) blocks or poly(substituted styrene) blocks per polymer molecule, or a polymer having at least 40 wt % repeat units from ethylene, or combinations thereof. From the tables it was clear that compositions comprising selectively hydrogenated block copolymers, having poly(styrene) blocks and poly(butadiene) or poly(isoprene) blocks before hydrogenation, could not be foamed with water. On the other hand it appeared that compositions comprising similar unhydrogenated block copolymers could not meet the heat resistance and UV resistance requirements.
From U.S. Pat. No. 6,127,444 a polymeric compound is known comprising (a) 100 parts by weight of a block copolymer comprising at least two external monovinyl aromatic hydrocarbon blocks and at least one internal hydrogenated conjugated diene block, wherein the total monovinyl aromatic hydrocarbon content is from 20 to 50% by weight and the total apparent molecular weight is from 140,000 g/mol to 400,000 g/mol; (b) 50 to 250 phr of a plasticiser (c) 10 to 100 phr of a polybutene 1 polymer having a melt index at 2.16 kg/190 DEG C. of from 0.05 to 400; (d) a blowing agent. That invention further relates to use of the compound for the preparation of foamed compounds; to a foaming process; to a masterbatch blend; to a foamed compound; and to articles containing the foamed compound. The final properties of foamed articles derived from said compositions, have appeared to be unable to meet the present combination of requirements, and in particular the heat resistance.
From IT 1317261 a process was known for the manufacture of elastomeric foam and the manufacture of stoppers and corks, by mixing at 1 6-2MO° C. a first component, comprising one or more thermoplastic elastomers, a plastomer and plasticizers, with a second component, comprising an elastomer containing at least one blowing agent, followed by compression moulding at 180-210° C. The blowing agent was neat or modified azodicarbonamide or mixtures of NaHCO3 and citric acid. The elastomers were styrene-ethylene-butylene copolymer (SEBS), styrene-ethylene-propylene copolymer (SEPS or SEEPS) or styrene-butadiene (SBS). The plastomer was selected from polypropylene, propylene copolymers, ethylene-vinyl acetate copolymer or LDPE. The plasticizer was mineral oil. The moulded products had a Shore A hardness of from 65-95. However, such foamed compositions appeared unable to withstand mechanical stresses at temperatures above 70° and were shown to be too hard when used for e.g. weatherstrips.
Similar products are known from WO 0102263, which provides a synthetic bottle stopper made from a foamed thermoplastic elastomer composition comprising: a) one or more thermoplastic block copolymers c) a blowing agent, and optionally d) one or more plasticisers, characterised in that the composition further comprises b) one or more branched polyolefins having a melt flow index of from 0.05 to 400 (at 2.16 kg/190 DEG C., determined in accordance with ASTIVD 1238).
From WO 0026103 an easily removable synthetic closure is known that is suitable for removable insertion into a bottle or container. In one embodiment, the synthetic closure comprises a thermoplastic elastomer and a metallocene catalyzed ethylene/alpha-olefin copolymer. In another embodiment, the synthetic closure is made from a composition formulated from the ingredients comprising: a thermoplastic elastomer that comprises a styrenic block copolymer; an ethylene/alpha-olefin copolymer; a polypropylene polymer; and a blowing agent; and wherein the closure has a Shore A hardness ranging from 60 to 84. The synthetic closure may further comprise an extending oil and/or a processing additive. In alternative embodiments the compositions suitable for forming the synthetic closures of the present invention optionally include thermoplastic elastomer materials such as, for example, thermoplastic polyurethane elastomers (i.e., TPUs), polyolefin-based thermoplastic elastomers (i.e., TPOs), thermoplastic elastomers based on dynamically vulcanized elastomer-thermoplastic blends (i.e., TPVs), thermoplastic polyether ester elastomers, thermoplastic elastomers based on halogen-containing polyolefins, and thermoplastic elastomers based on polyamides.
It will be appreciated that there is still a growing need for thermoplastic foamable compositions which can be efficiently processed into flexible, heat resistant, closed cell extruded articles of difficult sophisticated profiles, wherein the foamed material has a regular cell structure in all directions and without any substantial scrap material. Accordingly, it is an object of the present invention to provide an improved soft, low density thermoplastic elastomeric foam, which shows moreover an attractive compression set and water absorption, as specified herein before.
As result of extensive research and experimentation such foamable compositions aimed at have now surprisingly been found.